Drilling fluid



3.... ill" L Patented Feb. 5, 1952 2,584,768 DRILLING FLUID Walter. J. Weiss, Rolling Hills Area, Caliii, as,-

signor to Texaco Development Corporation, New York, N. Y., a corporationv of Delaware No Drawing. Application July 20,1949, SerialNo. 106,501

16 Claims. 01. 252-85) This invention relates to. drilling. muds and. the preparation and control of such as employed in the drilling of wells. More specifically, the invention relates to a method of. controlling. the colloidal and physicalproperties. of: drilling mud so as. to maintain it in the. mostv desirable condition for use.

This application is a continuation-impart of application, Serial No. 35,061, filed June 2.4, 1948., nowUnited States Patent No. 2,551,355, dated May 1. 1951 by Walter J. Weiss andentitled Imprcvements. in Drilling Fluid.

.Drilling muds or fluids, as they are. sometimes called.v are used. in the drilling of wells for tapping; underground collections of oil, gas, brine, or water. Such muds have difierent, functions, the most. important of which are to assist in the removal of cuttings from the well, to seal, off formations: of gas, oil or water which may be en! countered. at diiierent levels, to lubricate the drilling tool and the drill pipe which carries the tool, and to hold the cuttings in suspension in event of shutdowns in. drilling.

Drilling muds are essentially mixtures of. finely divided solids, such as clay and water, usually so compounded that they weigh about pounds per gallon. When found necessary to increase the specific gravity of a. particular mud, it is. customaryto add thereto finely divided materials of high specific gravities, such. as iron oxide, barytes, litharge, and the like.

The solid phase of a drilling mud consists of colloidal and non-colloidal particles. The colloidal: particles are responsible for the colloidal character of the drilling mud and the existence of such muds as essentially colloidal dispersions. An ideal drilling mud: is a thixotropic colloidal ,-..system, i. e., a fluid, which on agitation, as. by

pumping-or otherwise, has a relatively low viscosity and is free flowing, but when agitation is stopped, sets or gels. This gel action is sufficientyl slow to permit the cuttings to settle two or three feet before the gel structure which is developing during this time isstrong enough to support them. As used herein, the term thixotropic drilling mud" is intended to mean a drill,- ing fluid having the proper viscosity, the proper gel rate, and proper gel strength. When such a drilling fluid is circulated through a. well bore, it

has-a sufiiciently high viscosity to carry the cuttings and sand from the bottom of. the hole to the surface and it has a, sufllciently low gelling rate toallow the cuttings and sand to settle infa settling pit. On standing ina quiescent state, it develops suflicient gel; strength to-prevent the settl-ing oi the cuttings, sand, or barytes, etc., in the well bore itself when it becomes necessary to discontinue circulation for any appreciable. period or time. Sucha mudis also characterized by'its ability toform a mud cake on thebore liole'wal thereby assisting in sealing oil the traversed formations and inhibiting loss of water from the mud.

The use of a drilling mud which is non-thixotropic is attended. by many disadvantages, all of which are well-known to those skilled in the art. Such a mud either develops no gel at all, or gels rapidly enough. to remain in a plastic state while in motion. The former condition results in the settling of suspended solids at the bottom of the bore hole during periods of discontinued circulation. On the other hand, a. drill fluid which gels too rapidly is diificult to maintain free of cuttings and sand. Such a drilling mud of adequate viscosity at normal circulation rate easily becomes gas cut because of the recirculation of gas bubbles trapped by the rapid-forming gels or flocks. This is particularly dangerous in cases where a bore hole traverses or encounters high gas pressures because the gas cutting of the mud may so reduce. the hydrostatic head of the drilling mud in the bore hole as to result in the blowing out of the well.

Drilling muds are generally prepared by suspending clays in water, those clays being selected which will yield thixotropic colloidal system's. Such clays contain in varying amounts complex colloidal alumino-silicates. which are essentially acids whose anion is a micell of the general formula.

where X is approximately 1, Y is approximately 3, and Z may vary over wide values.

Although drilling fluids having various thixotropic properties may be prepared by the use of suitable clays, these desirable properties are lost in varying degrees; during the penetration of certain shales, clays, and water-bearing formations. Such deterioration may involve the conversion or a monovalent ion clay into an acid clay or a multivalent ion clay. The former occurs when the thixotropic drilling mud encounters, acid strata; the latter, which is the most common, occurs when the drilling mud encounters strata of calcium and magnesium clays or soluble compounds. Under such circumstances a phenomenon known as base exchange occurs whereby the monovalent ion clays are converted into multivalent ion clays and thereby rendered more sensitive to flocculating impurities.

,F-locculation or coagulation of any of the types of clays by flocculation materials such as salt encountered during drilling and the rapid accumulation of colloidal matter from penetrated shales or clays increases the viscosity of the mud and its gel strength, undesirably. Dilution of the mud with water, a frequently attempted remedy, is particularly undesirable if high gas pressures are encountered. since the specific gravity of the permitted any deterioration of the component in the mud materially reduces component. I 7

It is an object of the present invention to provide a drilling mud which possesses the aforesaid desirable thixotropic properties at the begin ning of its use and is capable of retaining those properties in substantially the original degree during use, regardless of the type strata encountered in the drilling.

Another object of the invention is the provision of a compound capable of preserving any added fermentable or otherwise spoilable content of a mud against such deterioration. A further object of the invention is the provision of a novel method of drilling wells coupled with the use of a fluid capable of retaining substantially the same desirable characteristics throughout the entire operation.

Further objects and advantages of the present invention will appear from the following description and attached claims.

In its broader aspect, the invention involves the use of complex alkali metal'heavy metal polyphosphates or reactants which go to make such complexes in drilling muds. More specifically, the invention involves the use of such complexes as are effective in preserving the fermentable or otherwise spoilable content of drilling muds andpreventing it from such deterioration.

In describing the invention, reference is first made to a known complex metal polyphosphate, namely, sodium cupric pyrophosphate, which is available commercially. This compound is considered to be of the probable formula NazCuPzOv. This particular compound when tested in a typical drilling mud such as 1:1 Rogers Lake-McKittrick light stock was found to be an effective viscosity reducing agent. This mud was formed of equal parts by weight of McKittrick light drilling mud clay and Rogers Lake drilling mud clay mixed with tap water to a 600 R. P. M. 77 F. Stormer viscosity of about 50 centipoises. The mud had a starch content of 12 lb. per A. P. I. bbl. (42 gallons) and was allowed to incubate at 130 to 140 F. over a 14 day period. The following table indicates the results obtained, the indicated viscosities being measured in centipoises at 600 R. P. M. at '7'7" F.-on a Stormer-type viscosimeter wherein changes had been made to improve the control of the times and rates of rotation.

Viscosity #N82Cl1PzO7 At end of per A. P. I. bbl. Original Highest Lowest 14 day test (42 gal.) period Untreated mud. 68 97+ 68 1 97 on 7th day and rising.

The same agent has given excellent results with regard to Water loss as measured in cc. per hour on a multiple cell filter press using paper as a filter base, operating at 100 p. s. i. having a the beneficial effect of the of about 3.5 cc./hour, became sour and showed a water loss of 6.5 cc./hour between the 7th and 8th days of the test period with the rate of water loss rising. The same mud, treated with /2 lb./A. P. I. bbl. of sodium 'cupric pyrophosphate showed no increase in fluid loss up to the 14th day and did not reacha 6 cc./hr. loss until the 28th day of the test period. With 1 lb./A. P. I. bbl., there was no increase in fluid loss during the first 14 days and on the 28th day was less than 5 cc./hr.

While this commercial sodium cupric pyrophosphate appeared to be relatively insoluble in water, the addition of ammonium hydroxide rendered the insoluble material more soluble and gave the intense dark blue color similar to that characteristic of the copper ammonium complex ion. This soluble product was tested as both a viscosity reducing agent and a starch mud preservative. Its efliciency in either respect did not appear to be affected.

However, the additional use of the ammonium hydroxide has been found to be advantageous. In the use of starch-containing drilling muds, even though preservatives are used, there seems to be a small amount of starch deterioration, which liberates acidic materials. This tendsto lower the pH of the mud over a period of time. In one case, the manufacturer of a commercial preservative recommends holding the pH of vthe mud between 8.3 and 9.0 by the use of caustic soda. The use of caustic soda with a conventional copper preservative results in the precipitation of the copper as copper hydroxide which causes the mud to sour immediately. This is not the case when ammonium hydroxide is used.

The use of ammonium hydroxide for pH control is also advantageous in that it affords a convenient and reliable method for maintaining the desired stable pH range outside the zone of greatest bacterial activity which is at a pH between 6 and 8. Any pH above or below this zone tends to suppress any rank bacterial growth. Substantially equally good results in the reduction of .viscosities of drilling muds have been secured by charging such muds with the reaction products of approximately stoichiometrical portions of a polyphosphate selected from the left column of the following table and a metal, compound selected from the right column:

, Polyphosphates Heavy Metal Compounds Sodium tetraphosphate, NaiiP4On." CuSO CuCOaCu(OII)| Malachite. Sodium triphosphate, Na5PaOw AgNOz.v

Sodium hexametaphosphate,

NasPsOm Sodium pyrophosphate, NmP;O1.-

Disodium dihydrogen pyrophosphate, N8zHzPzO1 NiGlz.

(1) N3.4P2O7+MSO4 N azMIPzOv-i-N a2SO4 NaziH2P2O7+MSO4- Na2MP2O7+H2804 NasPiO13+MSO4. NaaMBzOrH-NazSOs N aeP4O13+2MSO4+ N azM2P4O13+2N azSOa- NasPcO1s+MSO4- Na-i1VIP6Oia+NEZSO4 NasPsOm+2MSO4- Na2M2P6O1sl-2Na2SO4 NaP3O10+MSO4- Na3MP3O1c+Na2SO4 Na5P301o+2MSO4 NaM2P301o+2Na2S04 Neutralization of meta and pyrophosphoric acids with varying amounts of metal carbonates, oxides, hydroxides, or mixtures thereof, to yield intermediate metallic acid salts together with sufficient quantities of basic alkalimetal compounds.

Of the above, Equations 1, 3', 6, 7, and 9 are recognized reactions. Equation 2 is open to question as being exactly as represented since the reactions of Equations 1 and 2 with the same metallic salt sometimes give slurries of somewhat different soiubilities. This may be only a pH effect due to the acid nature of the sodium acid pyrophosphate.

Equation 4 appears to be a sequestering reaction and in Equation 5 a partial saturation of the Na2(NA4(PO3)s) formula may be correct or the reaction product may consist of a mixture of NazMzPsOm and unreacted NasPeOm.

Equation 8 is a possible reaction which could result in the formation of an equimol mixture of the neutral salt MsPsO-zo with the sequestering reaction product NasMPaoio In the experimental work, the reaction products shown below (some perhaps hypothetical but nevertheless eifective) were produced from the reactants indicated:

NazCuPzOq (from 9.38 g. Na4P2O-1 and 8.80 g.

'CuSOaSHzO) NazCuPaOw (from 9.54 g. NasPzOio and 6.48 g.

CuSOa5H20) Na2CuzP4O13 (from 9.30 g. N38P4013 (Quadrafos) and 9.88 g. CuSO4.5H2O) I NazCuzPsOm (from 9.46 g. NasPsOm (Calgon) and 7.70 g. CuSO4.5H2O) NazCuPzO7 (from 6.28 g. H4P2O7, 3.90 g.

CuC03.Cu(OH) 2 and 1.87 g. NazCOs) Na2HgP2O7 (from 6.32 g. Na4P2O'r and Hgclz) NaiHgP4O13 (from 7.53 g. Nat-P4013 (Quadrafos) and 4.35 g. HgClz) NazNiPzOv (from 9.54 g. Na4PzO7 and 8.53 g.

'NiClaGHzO) Na2Ag4P40l3 (from 5.81 g. Na6P4o13 (Quadrafos) and 8.39 g. AgNOs) :rIn each case, the theoretical amounts of polyphosphate and metal salts which would react to form 10 grams of the complex were used. The polyphosphate was dissolved or suspended in 80 to 90 ml. distilled water, the metal salt added and themixture shaken untilthe reaction appeared to be complete. Distilled water was added to bring the volume up to 100 ml., all chemical additions thereafter being based'on the premise that 100 ml. 01' the solution or slurry contained 10 gramsof the desired reaction product, i. e., the complex.

There is definite proof that the reaction prod ucts in each case include complex alkali'metal heavy metal polyphosphates or possess thecha'racteristics thereof.

Selecting Equation 1 by way of example and using the amounts of reactants indicated, the following equation is secured:

N84P207 CHS.O4.5HQO-)ITB2CHP107 N85 04 5H2O 9.38 g. 8.80 g. 10.00 g. 5.01 g. 3.17 g.

If there was noreaction, the final m1. of mixture would contain only 9.38 gms. of tetrasodium pyrophosphate and 8.80 grams of copper sulfate. At high chemical concentrations, this tetrasodium pyrophosphatewill overload the starch mud, and the copper sulfate, even at low concentrations, will cause severe flocculation of the mud. Neither occurred. On the contrary, mud having a viscosity of 51.9 cp. as indicated in the following table was reduced in viscosity to 18.0 cp. by the use of 0.5 gram" of the hypothetical (or actual) complex per 100 m1. of stock mud. This is believed to clearly indicate the formation of the complex.

Assuming the reaction to 'go' as shown, the final 100 ml. of solution contains 10 grams of NaZCUPZO'I and 5.01 grams of sodium sulfate. Sodium sulfate is notoriously detrimental to stock mud and causes flocculation thereof even at very nominal concentrations. However, such flocculation does not occur with this reaction product; It is, therefore, considered that while the reaction products as indicated above may have been formed, the complex polyphosphate is a sufliciently powerful viscosity'reducing' agent to offset the detrimental effects of the other re-' action product such as sodium sulfate.

The same conditions can be illustrated with the other reactions.

All the above actual products or reaction mixtures were tested to determine their efiect on the viscosity of a l':1 Rogers Lake-McKittrick light stock mud at 600 R. P. M. and 77 F. in a Stormer-type viscosimeter. No starch was used in the mud. The results are reported in the following table.

Stormer Viscosity at 600 R. P. M. and 77 F.Grams of Chem. (dry basis) per Compound 100 ml. of Stock Mud I Untreated 0. 010 0. 050 0.100 '0. 500

(711. C12. Cp. 0p. 0p.

NazCuPzOy 51. 9 44. 2 28. O 20. 6 18.0 50. I 44. 9 27. l 25'. 3 l7. 3 40. 3 3718 I 21. 9 22. 2 14.3 45. 2 42. 9 33. 9 29. 5 17. 3 =14. 8 42. 6 25. 8 20. 7 l7. 8 5i. 9 47. 7 30. 5 25. 5 17'. 0 44. l I 39. 8 30. 9 25. 5 16. 8 54. 6 45. 9 I 27. 6 24.1 21'. O 45. o I 43. 2 I 31'. 3 2e. 3- '17. 5

1 FY0111 N84Pz07 and ou o jflzo. 2 From H1P207, CuCO3.Cu(OE)2, and NaQCOu.

The above clearly indicates the high efficiency of the reaction products in controlling the viscosity of the drilling mud. a

To summarize, it will be noted that the reactants are mixed in'approximately the proper stoichiometric-proportions and the reaction *oducts charged to the drilling mud. In some .ses, it may be possible to charge the reactants rectly to the mud in the desired proportions 1d form the reaction products directl therein. reforming prior to charging is preferred beluse of the ability to better observe and con- 01 the reaction. The phrase approximately oichiometric proportions as used herein is .tended to include those proportions whereby 1e desired complex metal polyphosphate is lrmed such as NazCuPzO-z, Na4Ag(PzO7)a and izHg(PzO7)3. This usually necessitates the use i a slight excess of the alkali metal polyphoshate which apparently functions to dissolve 1e otherwise insoluble polyphosphates and enbles theproduction of the metal complexes.

When the polyphosphate and the selected ietal compound are mixed prior to charging to ie drilling mud, a slurry is sometimes formed. his slurry may be charged to the drilling mud s is. However, in some cases it has been found cat sufiicient ammonia can beadded to render he mixture clearer, the precipitate or suspenlon apparently being rendered more wateroluble. roducts of the initial reaction, thereby renderrig them more complex or whether the ammonia unctions only to effect dissolution of the solids unknown. The advantages of adding ammoiium hydroxide have already been discussed.

It has also been, found that the complexes lisclosecl herein are particularly valuable as tarch (pregelatinized) mud preservatives. Their use in the preservation of similar com- )ounds such as gelatin, gum tragacanth, agar, :asein, glue, soy bean glues and albumin is also :ontemplated.

By way of example, about 1 lb. of commercial .odium cupric pyrophosphate was added to an A. P. I. bbl. (42 gals.) of starch mud and the sample incubated with an untreated blank of ;he same mud. The untreated sample soured in eight days whereas the treated sample was still sweet after a period of two weeks. In another test involving a 1 bbl. mix of a 12# A. P. I. bbl. starch-containing mud, the mud was still sweet after being run for 6 weeks, 24 hours per day, in a pilot scale, mud circulation system. The preservation of the starch is particularly desired to preserve the low filtration rate (water-loss) of the mud. All the aforementioned complexes are substantially as effective as the sodium cupric pyrophosphate already discussed.

From the preservative tests conducted thereon, it is believed these complexes function best when charged initially in relatively large amounts supplemented by small charges at regular intervals. This method can be termed a quick kill method. This is particularly true in the case of the copper and nickel complexes. The mercury and silver complexes exhibit more sustained killing effect and are effected at lower concentrations. This is believed due not only to a higher degree of toxicity of the mercury-and silver-containing complex ions but also to the fact that the ions may not be as effectively adsorbed by the clay micelle.

In all cases, it is desirable to use a continual treating method. Small percentages of the compounds added initially do not appear to be effective as preservatives. It is desirable that an amount in excess of 0.5 lbs. (dry weight) per A. P. I. bbl. of mud be used initially for an initial quick kill effect. This is in excess of 0.15% by weight of the total weight of the mud stream.

Whether the ammonia enters into the Later and periodic charges are added to continue the treatment. An initial charge of 1 to 3 lbs. per bbl. followed by 1/9 lb. per tour (8 hr. shift) per bbl. of starch mud has been found satisfactory in pilot runs.

. Thus, the single complex has been found to perform a dual function, the last named function, i. e., the preservation function, being performed without the addition of any chemical other than the complex required to accomplish the first function, i. e., desired viscosity reduction.

The amount of agent or additive added to a particular mud depends upon numerou factors such as the type of mud, the amount of improve ment or the degree of protection that is desired in the drilling mud, and the conditions likely to be encountered. It has been found, however, that in most cases an amount Within the range of 0.01% to 1.00% by weight will produce the desired result. Overloading may occur in some cases at the higher value and it may be necessary to lower the top limit for those cases to 0.50%.

For preservative control, an amount in excess of 0.5 lb. per A. P. I. barrel of starch mud has usually been found necessary. It has been found preferable to charge initially from 1 to 3 lbs. per barrel followed by lesser amounts at intervals throughout the period of use.

The invention may be practiced in a number of different ways. The drilling mud may be prepared by incorporating the desired amount of agent directly in a suspension of clay in Water, or the requisite amount may be added to a drilling mud which is flocculated in order to reduce its viscosity to a value at which the mudv can be used most effectively. The agent may 1 also be continuously added to a drilling mud during use to prevent any substantial change in its colloidal and physical characteristics.

It is to be understood that the complex polyphosphates disclosed herein as preservatives for starch and functionally-similar compounds susceptible of deterioration can be used also as recovery agents, 1. e., they can be added to a sour mud to preserve the starch content thereof against further deterioration. In one case where a 12 lb. per A. P. I. bbl. starch mud had soured to an extent to raise the viscosity from about 60 cp. to about '77 cp. in three days, the addition of only 1 lb. of sodium cupric pyrophosphate per A. P. I. bbl. on the third day controlled the viscosity so that it reached only about 81 cp. after 11 more days. Even better control could have been secured had the initial charge been followed by smaller charges at regular intervals.

While the term reaction products" used herein is intended primarilyto include the complex reaction product, such as sodium cupric pyrophosphate, it is also intended to include any other of the reaction products that may contribute to the improved results obtained.

Obviously many modifications and variations of the invention as above set forth may be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated in the appended claims.

Iclaim: v

1. An aqueous drilling fluid containing reaction products formed in aqueous solution from an alkali metal polyphosphate and a water soluble compound containing a heavy metal selected from the group consisting of copper, silver, mercury and nickel, in amounts sumcient to control the viscosity of said fluid, said compounds being -.used in approximately stoichiometric proportions .iwith the polyphosphate in slight excess to form a complex alkali metal heavy metal polyphosphate.

2. An aqueous drilling fluid containing reaction products formed in aqueous solution from sodium pyrophosphate and a Water soluble compound containing a heavy metal selected from the group consisting of copper, silver, mercury and nickel, in amounts suflicient to control the viscosity of said fluid, said compounds being used in approximately stoichiometric proportions with the pyrophosphate in slight excess to form a complex alkali metal heavy metal pyrophosphate.

3; An aqueous drilling fluid containing sodium cupric pyrophosphate in amount sufiicient to control the viscosity of said fluid.

- 4. An aqueous drilling fluid containing reaction products formed in aqueous solution from an alkali metal polyphosphate, a Water soluble compound containing a metal selected from the group consisting of copper, silver, mercury and nickel, and ammonia, the latter being added in suflicient amount to control the pI-l of the fluid, said polyphosphate and metal compound being used in approximately stoichiometric proportions with the polyphosphate in slight excess to form a complex alkali metal heavy metal polyphosphate, the latter being present in an amount sufficient to control the viscosity of said fluid.

5. An aqueous drilling. fluid containing reaction products formed in aqueoussolution from sodium pyrophosphate, a. water soluble compound containing a metal selected from the group consisting of copper, silver, mercury and nickel, and ammonia, the latter being added in sufficient amount to control the pH of the fluid, said pyrophosphate and metal compound being used in approximately stoichiometric proportion with said pyrophosphate in slight excess to form a complex alkali metal heavy metal pyrophosphate,

the latter being present in an amount sufficient to control the viscosity of said fluid.

6. An aqueous drilling fluid containing ammonia and reaction products formed in an aqueous solution from an alkali metal polyphosphate and a water soluble compound containing a metal selected from the group consisting of copper, silver, mercury and nickel, said compounds being caused to react in an excess of said polyphosphate over the stoichiometric requirement to form a complex alkali metal heavy metal polyphosphate, said reaction products being present in an amount sufiicient to control the viscosity of said fluid.

'7. An aqueous drilling fluid containing a spoilable component from the group consisting of carbohydrates and proteinaceous materials and reaction products formed in aqueous solution from an alkali metal polyphosphate and a water soluble compound containing a heavy metal selected from the group consisting of copper, silver, mercury and nickel, in amount sufiicient to control the viscosity of said fluid and prevent spoiling of said spoila-ble component, said compounds be ing used in approximately stoichiometric proportions with said polyphosphate in slight excess to form a complex alkali metal heavy metal polyphosphate.

8. An aqueous drilling fluid containing a ferznentable component from the group consisting of carbohydrates and proteinaceous materials and reaction products formed in aqueous solution from sodium pyrophosphate and a water soluble compound containing a heavy metal selected from the group consisting of copper, silver, mercury and nickeLin amount suiflcient to control the viscosity of said fluid and inhibit fermentation of said fermentable component, said compounds being used in approximately stoichiometric proportions with said pyrophosphate in slight excess to form a complex alkali metal heavy metal pyrophosphate.

9. An, aqueous starch containing drilling fluid containing sodium cupric pyrophosphate in amount suflicient to control the viscosity of said fluid and prevent fermentation of the starch content thereof.

10. An aqueous drilling fluid containing a fermentableccmponent from the group consisting of carbohydrates and proteinaceous materials and reaction products'formed in aqueous solution from an alkali metal polyphosphate, a water soluble compound containing a metal selected from the group consisting of copper, silver, mercury and nickel, and ammonia, the latter being added in suflicient amount to control the pH'of the fluid, said polyphosphate and metal compound being used in approximately stoichiometric proportions with said polyphosphate in slight excess to form a complex alkali metal heavy metal polyphosphate, the latter being present in an amount suflicient to control the viscosity of said fluid and prevent fermentation of said fermentable component.

11. An aqueous starch-containing drilling fluid containing reaction products formed in aqueous solution from sodium pyrophosphate, a water soluble compound containing a metal selected from the group consisting of copper, silver, mercury and nickel, and ammonia, the latter being added in sufilcient amount to control the pH of the fluid, said pyrophosphate and metal compound being used in approximately stoichiometric proportions with said pyrophosphate in slight excess to form a complex alkali metal heavy metal pyrophosphate, the latter being present in an amount sufiicient to control the viscosity of said fluid and prevent fermentation of the starch content thereof.

12. An aqueous starch-containing drilling fluid containing ammonia and reaction products formed in an aqueous solution from an alkali metal polyphosphate and a water soluble compound containing a metal selected from the group consisting of copper, silver, mercury and nickel, said compounds being caused to react in a slight excess of said polyphosphate over the stoichiometric requirement to form a complex alkali metal heavy metal polyphosphate, said reaction products being present in an amount suflicient to control the viscosity of said fluid and prevent fermentation of the starch content thereof.

13. In a process for drilling a well with well drilling tools wherein there is circulated in the well a water base drilling mud containing colloidal particles of clayey material suspended in suflicient water to render the same circulatable, the method of controlling the viscosity of said mud and minimizing the loss of fluid therefrom comprising the steps of admixing with said drilling mud reaction products formed in an aqueous solution from an alkali metal polyphosphate and a Water soluble compound containing a heavy metal selected from the group consisting of copper, silver, mercury and nickel, said compounds being used in approximately stoichiometric proportions with said polyphosphate in slight excess to form a complex alkali metal heavy metal polyphosphate, said reaction products being present in an amount sufficient to conl the viscosity of said drilling mud, and conting the wall of said well with the resulting lling mud.

v4. In a process for drilling a well with well lling tools wherein there is circulated in the il a water base drilling mud containing colial particles of clayey material suspended in ficient water to render the same circulatable, 2 method of controlling the viscosity of said [(1 and minimizing the loss of fluid therefrom nprising the steps of admixing with said drillf mud sodium cupric pyrophosphate in amount ficient to control the viscosity of said drilling id, and contacting the wall of said well with a resulting drilling mud. L5. In a process for drilling a well with well lling tools wherein there is circulated in the ll a water base drilling mud containing col- :ial particles of clayey material suspended .in iicient water to render the same circulatable d a. spdilable component from the group conting of carbohydrates and proteinaceous maials, the method of controlling the viscosity said drilling mud and preserving said spoille component comprising the steps of admixi z with the drilling mud reaction products rmed in an aqueous solution from an alkali :tal polyphosphate and a water soluble comund containing a heavy metal selected from e group consisting of copper, silver, mercury d nickel, said compounds being used in apoximately stoichiometric proportions with said lyphosphate in slight excess to form agcomex alkali metal heavy metal polyphosphate, id reaction products being present in an amount suflicient to control" the viscosity of said drilling mud and preserve said spoilable component, and contacting the wall of said well with the result.- ing drilling mud. 1

16. In a process for drilling a well with well drilling tools wherein there is circulated in the Well a water base drilling mud containing colloidal particles of clayey material suspended in sufficient water to render the same circulatable and a spoilable component from the group consisting of carbohydrates and proteinaceous materials, the method of controlling the viscosity of said drilling mud and preserving said spoilable component comprising the steps'of admixing with the drilling mud sodium cupric pyrophosphate in amount suflicient to control the viscosity of said drilling mud and preserve said spoilable' component, and contacting the wall of said well with the resultingdrilling mud.

WALTER J. WEISS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Larsen Mar; 13, 1947 

